if its auto that about what these cars give.. manual version do have higher figures.
small engine not necessarily fuel efficient.. low torque means you have to accelerate more to get your required speed. hence wasting fuel..
try driving under 2000rpm and see if it makes a difference..
also you should get the spray pattern of your injectors tested and get them ultrasonically cleaned. make sure that your injectors are not leaking petrol. are you sure the milage is real and not reversed as is the case with majority of cars?
give your chassis number to pakwheel member shazaib aka sharabi.. he may be able to get the real auction sheet details from japan.